3.
for the first time “第一次” (作状语) the first time “第一次”(相当于连词引导时间状语从句)
This
is the first time that…. “这是第…次作某事了” (从句中用完成时)
On
that day the scientist took us to the lab for the first time.
The
first time we met, she wore a pair of glasses.
This
is the first time that I have been here.